Tamkang Journal of Science and Engineering, Vol. 4, No. 4, pp. 227-238 (2001)
227
Analytical Models for Predicting the Pullout Capacity and
Interaction Between Hexagonal Wire Mesh and
Silty Sand Backfill
D. T. Bergado and C. Teerawattanasuk
School of Civil Engineering
Asian Institute of Technology
P.O. Box 4, Klong Luang
Pathumthani 12120, Thailand
E-mail: [email protected]
Abstract
Large pullout tests were conducted on hexagonal wire mesh
embedded in silty sand locally known as Ayutthaya sand to investigate
the soil reinforcement interaction. PVC-coated of hexagonal wire
mesh was tested with different applied normal pressures ranging from
35 to 105 kPa. The hexagonal wire mesh specimens with 80x100 mm
cell sizes were pulled at a rate of 1 mm/min. In the conventional
pullout test wherein the clamping system is outside the pullout box,
the deformation and movement of hexagonal wire mesh known as
necking phenomenon occurred simultaneously during the pullout
process. In order to reduce this phenomenon, the large pullout test was
modified to install the clamping system inside the pullout box
hereinafter called “in-soil pullout test”. The total pullout resistance of
hexagonal wire mesh reinforcement consists of two components,
namely: friction and bearing resistance. An elastic-perfectly plastic
model was used to simulate the friction resistance and relative
displacement relation of hexagonal wire mesh while a hyperbolic
model was applied to simulate the passive bearing resistance of the
individual bearing member. The bearing resistance is approximately 4
to 6 times greater than the friction resistance. The maximum pullout
resistances increased with increasing specimen lengths as well as the
applied normal pressures. The in-soil pullout resistances are about
50% greater than the corresponding results from previous
conventional pullout tests. Several analytical models for predicting the
pullout resistance of hexagonal wire mesh reinforcement have been
proposed and modified in this paper. These proposed analytical
models for predicting the pullout resistance and displacement relation
agreed with the laboratory test results reasonable well.
Key Words :
Hexagonal Wire Mesh, Bearing Resistance, Analytical
Model, Pullout Box
1. Introduction
Soil reinforcements in the form of strips, grids,
and sheets such as steel bars, geogrids, and
geotextiles, respectively, have been developed.
With respect to the type of reinforcement, two
design parameters, namely: tensile strength (when
embedded in soil) and anchorage resistance, need
to be established. For relatively low modulus soil
reinforcement, the load elongation response may
also be required. Several researchers such as
[1,2,5,6,11] have investigated the test methods and
228
D.T. Bergado and C. Teerawattanasuk
with backfill soil compacted to 95% of maximum
dry density in accordance with ASTM D698-91
(standard Proctor test). The pullout box has inside
dimensions of 1270 mm in length by 760 mm in
width by 508 mm in height. The pullout force was
applied by a 225 kN capacity electro-hydraulic
controlled jack through a steel reaction frame
mounted in front of the pullout box. The normal
pressure was varied from 35 kPa to 105 kPa. The
pullout rate of 1 mm/min [2] was constantly
adopted in all the tests.
In the conventional pullout tests conducted by
[13,15], the deformation and movement of
hexagonal wire mesh known as necking
phenomenon occurred simultaneously during
pullout process because the clamping system was
installed outside the pullout box as illustrated in
Figure 1. In order to reduce the effects of necking
phenomenon, the modified clamping system was
installed inside the pullout box hereinafter called
“in-soil pullout test” [8] as shown in Figure 2.
design equations for establishing design
parameters. A very important factor in the analysis
and design of soil reinforcement is the interaction
behavior between reinforcements and backfill soils.
Several researchers have studied on interaction
behavior between hexagonal wire mesh
reinforcement and various backfill materials in
both pullout and direct shear mechanisms of grid
reinforcements [7,12,14,15]. This paper mostly
deals with the research results of [8,13,15] under
the supervision of the first author concerning the
developments of the analytical models on the
interaction of hexagonal wire mesh reinforcement
and silty sand backfill.
2. Laboratory Pullout Tests
Silty sand backfill locally known as Ayutthaya
sand was used as backfill soil for the PVC-coated
hexagonal wire mesh reinforcement. The
properties of silty sand and the properties of
PVC-coated hexagonal wire mesh are shown in
Tables 1 and 2, respectively. The tests were done
Table 1. Index properties of silty sand backfill (Ayutthaya sand)
Mir
(1996)
Long
(1996)
Specific Gravity, Gs
2.68
2.66
2.69
2.65
2.67
Effective Size, D10 (mm)
0.22
0.09
0.18
0.21
0.22
Uniformity Coefficient, Cu
4.09
5.7
3.83
3.57
3.18
Coefficient of Curvature, Cc
1.21
0.9
1.29
0.92
0.99
11.0
10.0
11.7
11.5
11.50
Max. Dry Unit Weight, γd max (kN/m )
18.25
18
18.53
18.33
18.1
Angle of Friction, φ (degrees)
26.6
30
28
-
-
Properties
OMC, %
3
Teerawattanasuk Wongsawanon
(1997)
(1996)
Table 2. Properties of triple-twisted hexagonal wire mesh
Properties
PVC-Coated Type
Core Wire Diameter (mm)
2.70
Overall Wire Diameter (mm)
3.80
Cell Size, W x L (mm)
80 x 100
Wide Width In Air Tensile Test (kN/m)
- Mir (1996)
48
- Kabiling (1997)
44.80
- Wongsawanon (1998)
- Kongkitkul (2001)
with constrained rods
without constrained rods
44.10
42.67
44.83
Kongkitkul
(2001)
Analytical Models for Predicting the Pullout Capacity and Interaction Between Hexagonal Wire Mesh and Silty Sand Backfill
229
Boundary of Large Scale Pullout Box
Apparatus
760 mm
500 mm
Pull
Direction
Steel Clamp
Hexagonal cell in the centerline of the reinforcement
Hexagonal cell at the edge of the reinforcement
1100 mm
1270 mm
Figure 1. Deformation and necking phenomena of hexagonal wire mesh reinforcement during pullout process
Bondary of LArge Scale
Boundary of Large Scale
Pullout Box Apparatus
Pullout Box Apparatus
Twisted Members
Pullout
Direction
Outer Clamps
Steel Rods
In-soil Clamps
Transverse
Members
Figure 2. Clamping system used in laboratory in-soil pullout test
230
D.T. Bergado and C. Teerawattanasuk
3. Analytical Models for Predicting the
Pullout Resistance
The hexagonal wire mesh specimens indicated
that the necking phenomena occurred during the
pullout mechanism. Pullout resistance of soil
reinforcement system contains two components,
namely: friction and bearing resistances. For
hexagonal wire mesh reinforcement, the bearing
resistance was modeled by hyperbolic function [1,2]
which was modified and used in this study. The
friction resistance can be evaluated by
elastic-perfectly plastic model based on large scale
direct shear test results which were investigated by
[12,14]. The results showed a slight difference
when the displacement is less than 10 mm. The
basic parameters used for predicting the pullout
resistance and displacement curves in silty sand
were summarized in Table 3. The apparent
cohesion, c’ = 10 kPa and friction angle, φ’ = 30°
were taken from the large scale direct shear
conducted by [9] as tabulated in Table 1. The
summarized of Eip-values used in the analytical
modeling with different types of hexagonal wire
mesh and different applied normal pressures were
shown in Table 4. The proposed analytical models
for predicting the pullout resistance of the
hexagonal wire mesh are discussed in the
following sections.
Table 3. Basic parameters used for predicting the
pullout resistance and displacement curves
Backfill soil parameters
Table 4. Computed parameters used for predicting the
pullout resistance and displacement curves
(Kongkitkul, 2001)
Parameters
Normal pressure (kPa)
55
80
105
Ultimate bearing strength,
1545
σult (kPa)
Initial slope of pullout
resistance/normalized
3273
displacement curve, Eip (kPa)
2086
2628
3757
4130
3.1 Analytical Assumptions
In order to develop the analytical models,
several assumptions are required to simplify the
analysis. From the observation of the deformed
hexagonal wire meshes, the elongation of
hexagonal wires mostly occurred on the
transverse members (see Figure 2), while the
elongation occurred on the twisted members
(see Figure 2) was quite small and assumed to
be negligible. However, in the analytical
assumptions proposed by [13,15], the transverse
members have been rotated during the pullout
process corresponding to the necking
phenomenon of the hexagonal wire mesh
specimen as shown in Figure 1. By installing
the clamping system inside the pullout box, the
rotations of the transverse members are greatly
reduced. Therefore, it could be assumed that the
transverse members did not bend during the
pullout process because the necking of wire
mesh specimen was minimized and could be
neglected.
Silty sand
Cohesion, c’ (kPa)
10
3.2 Bearing Resistance of Hexagonal Wire
Mesh
Friction angle, φ’ (degrees)
30
3.2.1 Wongsawanon (1998) Model
Failure Ration, Rf
- Wongsawanon(1998)
- Srikongsri (1999)
- Kongkitkul (2001)
Diameter of transverse
member, D (m)
Length of single transverse
member, L (m)
Diameter of twisted member,
DT (m)
Length of twisted member, LT
(m)
Initial angle of transverse
member, α (degrees)
0.95
0.95
0.85
0.0038
0.06
0.0076
0.04
96
The hexagonal cells during deformation
created the resistance consisting of frictional
and bearing resistance. Thus, the relationship
between bearing resistance and displacement of
cell can also be related by considering the
deformation characteristic and movement of
single hexagonal cell as shown in Figure 3. In
accordance with the analytical model proposed
by [15], as shown in Figure 4a, the pullout
bearing resistance on element AB can be
expressed as follows:
L2 ⋅ sin(θ / 2) ⋅ sin(α / 2 −θ) ⋅ 3⋅ sin(α / 2 −θ / 2) (1)
Pb =
1 3 ⋅ L ⋅ sin(θ / 2) ⋅ sin(α / 2 −θ / 2)
+
Eip
D ⋅σult
Analytical Models for Predicting the Pullout Capacity and Interaction Between Hexagonal Wire Mesh and Silty Sand Backfill
Figure 4b shows the movement characteristic of
element CD. The movement occurred only at
point C, while point D is fixed at the same
location before starting the pullout. The bearing
resistance pressure formed into triangular
distribution, which can be determined from the
pullout bearing resistance as follows:
L2 ⋅ sin(θ / 2) ⋅ sin(α / 2 − θ)
1 2 ⋅ L ⋅ sin(θ / 2)
+
E ip
D ⋅ σult
Pb
l2
θ
"
A
ud
C
B
d
d
l2
θ
θ
α
A
θ
D
B
d
(2)
Figure 5 shows the comparison between
the laboratory pullout test results and prediction
results of PVC-coated hexagonal wire mesh
reinforcements. The predicted pullout force and
displacement curves agreed well with the test
data. However, the prediction results slightly
differ from the test results. The prediction of
pullout-load and displacement relationship
shows that the friction resistance is lower than
the pullout bearing resistance. This may be
attributed to the small effective frictional area
of the wire mesh compared to the total area of
influence. Moreover, there is low shear strength
at the interface between fill material and
reinforcement. The friction resistance is fully
mobilized when the pullout displacement
exceeds 20 mm while the bearing resistance is
partially mobilized. From the comparison
between the predictions and laboratory pullout
test results, the proposed analytical method can
be used to predict the pullout resistance and
displacement curve.
ud
90 + (θ−α)/2
α/2
l2 cos(α/2)
(a) Bearing resistance of surrounding soil on element AB of
hexagonal cell
C
d
σb
l2
θ
Pb
α/2
D
(b) Bearing resistance of surrounding soil on element CD of
hexagonal cell
Figure 4. Bearing resistance of surrounding soil on
hexagonal cell
40
4
Pullout resistance
(kN/m-wide)
Pull-out
Load (kN
/m-wide )
Pb =
231
Test result
Bearingresistance
Frictionresistance
Total pullout force
30
3
Normal Pressure = 49kPa
2
20
1
10
θ
d
l2
d
F
l1
0
0
E
Figure 3. Modeling of deformation and movement of
single hexagonal cell considering the necking
phenomena of hexagonal wire mesh specimen
10
20
30
40
50
60
70
80
90
Pullout
displacement
(mm)
Pull-out
Displacement (m
m.)
Figure 5. Prediction of pullout resistance and displacement
relationship of PVC-coated wire mesh
(Wongsawanon, 1998)
232
D.T. Bergado and C. Teerawattanasuk
3.2.2 Srikongsri (1999) Model
In the work of [13], the bearing
resistance was considered only in the pullout
direction with transverse members. The
bearing
resistance
and
displacement
relationship proposed by [15] has been
modified to investigate the mobilized bearing
resistance analytically. The relationship of
bearing force and displacement of a single
hexagonal cell based on hyperbolic model
were
divided
into
two
sources
of
displacements, namely: the bearing resistance
due to the movement of the cell and the
bearing resistance due to the cell deformation.
For the proposed analytical model proposed
by [13], the bearing resistance of an
individual member is needed. By the
combination of single transverse wire
movement and rotation, the bearing resistance
can be expressed as follows:
⎞
⎛
⎜
⎟
L⋅sinθ/2
Um
⎟ (3)
+
Pb = Lsin(α/2−θ) ⎜
1 2⋅ L⋅sin(θ/2) ⎟
⎜ 1 + Um
⎟
⎜ E D⋅σ E + D⋅ σ
ip
ult
ult
⎠
⎝ ip
The
displacement
mobilized
by
movement (see in Figure 6), U m , can be
expressed in terms of rotational angle of
single transverse member as follows:
(4)
U m = L cot β (sinα/2 –sin(α/2-θ))
The displacement mobilized by the
transverse element rotation or deformation in
each row can be geometrically related to the
rotational angle of the single transverse
member as shown in Figure 6. Hence, this
relationship can be written as:
Ud = L (cos(α/2-θ)-cosα/2)
(5)
where: θ is the rotational angle of a single
transverse member, Eip is the initial slope of
pullout bearing resistance, D is the diameter of
transverse member, Um is the displacement due
to movement, L is the length of single
transverse member, Ud is the displacement
due to deformation, α is the initial angle of the
transverse element (α = 96°), Εip is the initial
slope of pullout bearing resistance, σult is the
ultimate pullout bearing resistance which is
equal to σbm/Rf [4], σbm is the maximum
pullout bearing resistance from bearing
capacity equation, Rf is the failure ratio (Rf =
0.95 ), β is the angle of nodal movement of
single transverse member inclined from
pullout direction to the center of
reinforcement.
The pullout resistance for PVC-coated
hexagonal wire meshes is computed using the
proposed analytical model. The calculation
was also separated into friction and bearing
resistances by applying the hyperbolic and
elastic, perfectly-plastic constitutive models,
respectively. The necking phenomena of
hexagonal wire mesh were considered in the
analytical model. The predicted mobilized
bearing resistance curves have similar shape
to the total pullout resistance curves. The
computed pullout resistance of bearing and
friction of both wire mesh types were
combined into a total pullout resistance for
each different level of applied normal
pressures. The calculated values are validated
corresponding to the plots of pullout test
results as illustrated in Figure 7 for
PVC-coated wire mesh at the applied normal
pressure of 90 kPa. The predictions are very
close to the measured values. Slight
differences were observed because of the
limited assumptions of analytical method as
well as the scatter of test data.
According to the study [13], the
calculated results can explicitly explain how
the bearing and friction forces were mobilized.
Normally, the friction and bearing resistances
in hexagonal wire mesh cannot be directly
observed by using the conventional laboratory
pullout test. The predicted curves indicated
that friction resistance is 28% of the bearing
resistance for the PVC-coated hexagonal wire
mesh. The friction resistance for the
PVC-coated hexagonal wire mesh is 21% of a
total pullout resistance. The primary
resistance obtained from the interaction
between soil and reinforcement is mainly
caused by the bearing forces acting on the
transverse members. The secondary resistance
is the friction resistance produced by the
surface area of all members that move relative
to surrounding soil.
Analytical Models for Predicting the Pullout Capacity and Interaction Between Hexagonal Wire Mesh and Silty Sand Backfill
233
Pullout
Pullout direction
A'
θ
θ
Ut
L
L
A
B'
β
Ud
α
B'
L
β
L
B
Um
B
Figure 6. Deformation characteristics of single transverse wire in hexagonal wire mesh reinforcement with the consideration of
necking phenomena (Srikongsri, 1999)
60
predicted friction
predicted bearing
predicted total
test result
Pullout
resistance
(kN/m)
Pullout
resistance
(kN/m-wide)
50
Normal Pressure = 90 kPa
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90
Pullout displacement
displacement (mm)
(mm)
Figure 7. Predicted pullout resistance of PVC coated wire mesh in silty sand (Srikongsri, 1999)
100
234
D.T. Bergado and C. Teerawattanasuk
3.2.3 Kongkitkul (2001) Model
In the study of [8], the pullout clamping
system was modified and installed inside the
fill material hereinafter called “in-soil pullout
test”. Consequently, the effect of the necking
phenomena was reduced to negligible level
and the lateral movement of hexagonal wire
mesh can be assumed to be zero. Therefore,
the analytical models previously proposed by
[13,15] and required some modifications to
clearly predict the pullout resistance and
displacement results for the in-soil pullout test.
Hence, Equations 1, 2 and 3 have been
modified due to the difference in the
deformation characteristics. According to the
combination of single transverse wire rotation
and/or elongation and movement in the
pullout direction, the bearing resistance in
each segment of transverse wire can be
expressed in the following forms:
⎡
⎤
⎢
⎥
Um
L'sin θ 2
⎥
Pb = L'sin ( α 2 −θ) ⋅ ⎢
+
1 2 ⋅ L'sin θ 2 ⎥
⎢ 1 + Um
+
⎢ Eip D⋅σult Eip
D⋅σult ⎥⎦
⎣
(6)
The elongated length of each transverse
member during the pullout tests can be
calculated as follows:
L' =
L ⋅ sin(α / 2)
sin(α / 2 − θ )
(7)
Furthermore, the displacement due to
transverse member movement in the pullout
direction as shown in Figure 8, U m , can be
assumed to be the linear function of the
amount of elongation in the transverse
member, dL, as follows:
Um = k ⋅ dL= k ⋅ (L'−L)
(8)
and
⎡ sin( α / 2 )
⎤
Um = k ⋅L⋅⎢
− 1⎥
⎣ sin( α / 2 − θ )
⎦
(9)
Then, the displacement of the transverse
member related to the rotation and elongation,
U d , can be expressed as follows:
Ud =
L⋅ sin(α / 2) ⋅ cos(α / 2 −θ)
− L⋅ cos(α / 2)
sin(α / 2 −θ)
(10)
where: D is the diameter of transverse
member, L is the original length of each
transverse member, k is the coefficient of
linear function, L′ is the elongated length of
each transverse member, σ ult is the ultimate
pullout bearing resistance, E ip is the initial
slope of pullout bearing resistance curve, U m
is the displacement of each transverse member
due to movement in the pullout direction, U d
is the displacement of each transverse member
due to rotation and elongation, α is the
original apex angle of transverse member
(α = 96°), θ is the rotational angle of a single
transverse member.
The predicted bearing and frictional
resistances of the PVC-coated hexagonal wire
meshes were combined together to obtain the
total pullout resistance. The predicted bearing
and frictional resistance and displacement
curves and the predicted total pullout
resistance increased with increasing applied
normal pressure. The predicted total pullout
resistance and displacement curves from
analytical model can be favorably compared
with the corresponding experimental results
from the in-soil laboratory pullout tests at the
applied normal pressure of 55 kPa as shown in
Figure 9. In addition, it was found that the
bearing resistance is approximately six times
the frictional resistance for PVC-coated
hexagonal wire mesh.
Referring to Figure 9, the predicted
pullout resistance and displacement curves
showed that the frictional resistance was 14%
of the total pullout resistance for PVC-coated
hexagonal wire mesh. Consequently, the
bearing resistance was 86% of the total
pullout resistance for PVC-coated hexagonal
wire mesh. The variation of applied normal
pressure had no effect on the fraction of
bearing and frictional resistances. The bearing
resistances predicted from the analytical
model significantly depended on the initial
slope of normalized bearing resistance and
displacement curve, E ip . The calculated
procedures to obtain E ip values were discussed
on [1]. For silty sand backfill, the E ip values
varied from 3273 kPa to 4130 kPa (see Table
4) corresponding to the applied normal
pressures.
Analytical Models for Predicting the Pullout Capacity and Interaction Between Hexagonal Wire Mesh and Silty Sand Backfill
235
Pullout direction
A'
θ
θ
Ut
L'
A
B'
L'
Ud
α
B'
L
Um
L
B
B
Pullout resistance (kN/m-wide)
Figure 8. Deformation characteristics of single transverse wire in hexagonal wire mesh reinforcement
without the consideration of necking phenomena (Kongkitkul, 2001)
80
70
60
50
40
30
20
10
0
Test result
Predicted pullout resistance
Predicted bearing resistance
Predicted frictional
0
5
10
15
20
25
30
35
40
45
50
Displacement (mm)
Figure 9. Predicted pullout resistance of PVC-coated hexagonal wire mesh in silty sand (Kongkitkul, 2001)
3.3 Frictional Resistance of Hexagonal Wire
Mesh
Based on the large scale direct shear
laboratory test results conducted by [12,14], the
confirmation of friction resistance was fully
mobilized when the reinforcement was pulled by
10mm. The shear stress on the interface between
the reinforcement and material was assumed to
follow the elastic-perfectly plastic model.
Therefore,
the
friction
resistance
and
displacement curve can be simply related to the
elastic-perfectly plastic model (as discussed on
[3]). The frictional resistance at the different
pullout displacements can be calculated by
assuming an average relative displacement. In
general, the frictional resistance in hexagonal
wire mesh generally was separated into two parts.
The first part established from the single
transverse member while the second part resulted
from the twisted member. The frictional resistance
in twisted member is related to shear stiffness,
relative displacement and frictional area. Hence,
the same equation applied in the study of [8,13,15]
can be written as the following forms:
(11)
Fs = ks.ur.(π.DT.LT)
In the case of frictional resistance on
transverse member, both the rotation and
elongation of the transverse members have the
influence on the deformation, which will be
affected on the frictional resistance. The
elongations occurred in the transverse members
during the pullout test increase the frictional
resistance due to the increasing of frictional
surface area of the transverse members. Therefore,
236
D.T. Bergado and C. Teerawattanasuk
the frictional resistance on the transverse members
including the effect on elongation of the transverse
members can be expressed as follows:
Fs = ks.ur.(π.D.L′).cos(α/2-θ)
(12)
where: ks is the shear stiffness of the interface, LT
is the length of twisted wire, ur is the relative
displacement, L′ is the length of transverse wire
corresponding to θ angle, D is the diameter of
transverse wire and DT is the diameter of twisted
wire which is about two times of the transverse
wire diameter.
4. Discussion on Maximum Pullout
Resistance in Various Pullout
Test Programs
Maximum pullout load (kN/m)
The
maximum
pullout
resistances
corresponding to the applied normal pressures
are plotted in Figure 10 for PVC-coated
hexagonal wire mesh. From the test results of
[7,8], the maximum pullout resistances increased
with increasing the specimen lengths as well as
the applied normal pressures. Most specimens
80
70
60
50
40
30
20
10
0
failed by breakage, but for the 0.70 m long
specimens at the applied normal pressure of 55
kPa, the PVC-coated specimens failed by
slippage.
It can be seen that most of the in-soil
pullout resistances were greater than the ultimate
in-air tensile load. Since the clamp installed
inside the in-soil pullout box reduced the
necking phenomenon, greater pullout load can be
mobilized in the hexagonal wires due to the
bearing resistance from the surrounding soil.
Referring to Figure 10, the in-soil pullout
resistance where the clamping system was
installed inside the pullout box, approximately
increases 50% more than the conventional
pullout test results. Moreover, the pullout tests
from [10] can be referred as a modified tensile
strength test in which the effects of different
applied normal pressures can be taken into
account. Not much difference exists between the
ultimate wide-width in-air tensile load and the
maximum pullout load from [10] as presented in
Figure 10 because of the application of confining
pressure in the latter.
Tult = 44.8 kN/m (in-air tensile test)
Maccaferri (1997)
Kongkitkul (2001), L = 0.70 m
Kabiling (1997), L = 1.10 m
Kabiling (1997), L = 0.90 m
Kabiling (1997), L = 0.70 m
0
20
40
60
80
100
120
140
160
Applied normal pressure (kPa)
Figure 10. Relationship between pullout resistance of PVC-coated hexagonal wire mesh in silty sand (Kongkitkul, 2001)
5. Conclusions
Large conventional pullout tests and
in-soil pullout tests were performed in the
pullout box with inside dimensions of 1270
mm in length by 760 mm in width by 508 mm
in height were conducted on PVC-coated
hexagonal wire mesh embedded in silty sand
to investigate the soil reinforcement
interaction. PVC-coated wire mesh specimen
with 80x100 mm cell sizes was tested with
different applied normal pressures ranging
from 35 to 105 kPa at a pullout rate of 1
mm/min. The pullout resistance of the
hexagonal wire mesh reinforcement consists
of two components, namely: friction
resistance and passive bearing resistance. An
elastic-perfectly plastic model was used to
simulate the friction resistance and relative
displacement relation of hexagonal wire mesh
Analytical Models for Predicting the Pullout Capacity and Interaction Between Hexagonal Wire Mesh and Silty Sand Backfill
while the hyperbolic model was applied to
simulate the passive bearing resistance of the
individual bearing member.
The
maximum
pullout
resistances
increased with increasing specimen lengths as
well as the applied normal pressures. The
necking phenomenon occurred during the
pullout process could be greatly reduced to be
negligible amounts by installing the clamping
system inside the pullout box. Consequently,
the in-soil pullout resistances are greater than
the results from conventional pullout tests in
which the clamping system was installed
outside the pullout box. The friction
resistances with in-soil pullout clamping
systems are 14% and 21% for inside installed
clamp and outside installed clamp of the
pullout box, respectively, compared to the
total pullout resistance. On the other hand, the
bearing resistances compared to the total
pullout resistance for in-soil installed clamp
and outside installed clamp of the pullout box
are 86% and 79%, respectively. The bearing
resistance is approximately 4 to 6 times
greater than the friction resistance. The in-soil
pullout resistance approximately increases
50% more than the conventional pullout test
results conducted by [13,15] wherein the
clamping system was installed outside the
pullout box. The proposed analytical models
for predicting the pullout resistance and
displacement relation agreed with the
laboratory
experimental
test
results
reasonable well.
[5]
[6]
[7]
[8]
[9]
[10]
[11]
References
[1] Bergado, D. T. and Chai, J. C., “Pullout
force/displacement
relationship
of
extensible grid reinforcements,” Geotextile
and Geomembranes., Vol. 13, pp. 295-316
(1994).
[2] Bergado, D. T., Chai, J. C. and Miura, N.,
“Prediction of pullout resistance and
pullout force-displacement relationships for
inextensible grid reinforcements,” Soils
and Foundations., Vol. 36, pp. 11-12
(1996).
[3] Bergado, D. T., Voottipruex, P., Srikongsri, A.
and Teerawattanasuk, C.,
“Interaction
between hexagonal wire mesh reinforcement
and
silty
sand
backfill,” Canadian
Geotechnical Journal. Vol. 24, 26-41 (2001).
[4] Duncan, J. M. and Chang, C. Y., “Nonlinear
analysis of stress and strain in soil,” Journal
[12]
[13]
[14]
237
of Soil Mechanics and Foundation
Engineering Division. ASCE, Vol. 96, pp.
1629-1653 (1970).
Ingold, T. S., “Laboratory pullout testing of
grid reinforcements in sand,” Geotechnical
Testing Journal., Vol. 6, pp. 101-110 (1983).
Jewell, R. A., Miligan, G. W. E., Sarsby, R.
W. and Dubois, D., “Interaction between soil
and geogrids,” Proc. Symposium on Polymer
Grid Reinforcement in Civil Engineering,
Thomas Telford Ltd, London, U.K., pp. 19-29
(1984).
Kabiling, M. B., “Pullout capacity of
different hexagonal link wire sizes and
configurations on sandy and volcanic ash
(lahar) backfills,” M.Eng. Thesis No. GE
96-4, Asian Institute of Technology,
Bangkok, Thailand (1997).
Kongkitkul, W., “Numerical and analytical
modeling on pullout capacity and interaction
of in-soil pullout tests between hexagonal
wire mesh reinforcement and silty sand,”
M.Eng Thesis, Asian Institute of Technology,
Bangkok, Thailand (2001).
Long,
P.
V.,
“Behavior
of
geotextile-reinforced embankment on soft
ground,” D. Eng. Doctoral Dissertation No.
GT 96-1, Asian Institute of Technology,
Bangkok, Thailand (1996).
Maccaferri Asia, Terramesh System, “A
solution for soil-reinforcement,” Jakarta,
Indonesia (1997).
McGown, A., Andrawes, K. Z. and Kabir, M.
H., “Load extension testing of geotextiles
confined in soil,” Proc. 2nd Intl. Conf. on
Geotextiles, Las Vegas, Vol. 3. pp.793-796
(1982).
Mir, E. N., “Pullout and direct shear test of
hexagonal wire mesh reinforcements in
various fill materials including lahar from Mt.
Pinatubo, Philipines,” M. Eng. Thesis No.
GE 95-18, Asian Institute of Technology,
Bangkok, Thailand (1996).
Srikongsri, A., “Analytical model of
interaction between hexagonal wire mesh and
silty sand backfill,” M. Eng. Thesis No. GE
98-17, Asian Institute of Technology,
Bangkok, Thailand (1999).
Teerawattanasuk, C., “Interaction and
deformation behavior of hexagonal wire
mesh reinforcement at the vicinity of shear
surface on sand and volcanic ash (lahar)
backfill,” M. Eng. Thesis. No. GE 96-14,
Asian Institute of Technology, Bangkok,
Thailand (1997).
238
D.T. Bergado and C. Teerawattanasuk
[15] Wongsawanon, T., “Interaction between
hexagonal wire mesh reinforcement and silty
sand backfill,” M. Eng. Thesis GT 97-14,
Asian Institute of Technology, Thailand
(1998).
Manuscript Received: Jun. 1, 2001
And Accepted: Jul. 9, 2001